Contributions of Darwin
Watch the videos provided under Additional Resources to
Contributions of Darwin
Watch the videos provided under Additional Resources to learn more about Darwin, his voyage, Wallace, and the history. If you wish to learn more, you can watch the video explaining the Wallace line.
Natural Selection and Adaptations
Having watched the videos you have now understood that adaptations and natural selection are key in the process of evolution.
Now watch this video and answer the following
1.Explain the terms adaptation and natural selection.
2.Speculate whether the Natural selection __________ (increases / decreases) the adaptation of organisms to their environment over time.
3.Determine how natural selection explains the adaptations of organisms.
4.What is Darwin’s theory of evolution?
5.What happened in the case of peppered moths and industrialization?
6.What is the mechanism that results in variation within a population?
7.How do the black mice arise in the population – are they already present within the mice population or does the new traits arise “as needed”?
8.Why did the frequencies of the light-colored and dark-colored mice not change significantly at location A but did at location B? – Explain based on the concept of ‘the selective pressure of predators’.
Darwin, the Galapagos, and the Finches
We know that Darwin visited the Galapagos Islands and one of the key observations was regarding the finches on the islands. Watch this brief video to see how Darwin realized the differences in the finches.
1.How did the finches differ from each other?
2.Describe the basis for the differences observed in the finches of the Galapagos Islands.
3.Explain how natural selection played a role in this the case of finches of the Galapagos Islands.
The Evidence for Evolution
Watch the video and discover the evidence to support the theory of evolution
1.Direct Observations of Evolutionary Change
2.Homology
3.Fossil Records
4.Biogeography
Modes and Mechanisms of Evolution
The following video explains the mechanisms of evolution – directional, disruptive, and stabilizing selection.
Understand the concept of each type of mode of directional selection. Can you predict the mode of action for natural selection if given a scenario. Below are some examples. Give reasons for your answer
1.Mostly human beings tend to be of average height- not too many really short ones or really tall ones
2.In tigers, faster is always better so a tiger population will tend to get faster over time
3.In case of giraffes, there was a selection pressure against short necks, since individuals with short necks could not reach as many leaves on which to feed. As a result, the distribution of neck length shifted to favor individuals with long necks.
4.Suppose a plant of extremely variable height is pollinated by three different pollinators, one that was attracted to short plants, another that preferred plants of medium height and a third that visited only the tallest plants. If the pollinator that preferred plants of medium height disappeared from an area, medium height plants would be selected against and the population would tend toward both short and tall, but not medium height plants.
5.If thicker-shelled oysters are more resistant to breakage than thinner-shelled oysters, crabs will be less able to prey upon them, and thicker-shelled oysters will be more likely to survive to reproduce
6.Very light-colored or very dark-colored oysters might be more frequently preyed upon by shore birds, simply because they are more obvious on the oyster bar; as a result, the intermediate hues become more common
7.Light-colored oysters are more cryptic (coloration that allows an organism to match its background and hence become less vulnerable to predation or recognition by prey) and therefore, less easy for a predator to see because they match the rock color. Dark-colored oysters blend into the shadows cast by the rocks. In this case, intermediate-colored oysters would be most heavily preyed upon by the crabs, and very light and very dark oysters would survive to reproduce.
Understand the concept of convergent evolution.
Coevolution occurs in some species. One good example of coevolution is acacia ants and acacia plants. http://www.youtube.com/watch?v=Xm2qdxVVRm4
Speciation – How do we define species, how do they form, the speed/tempo, and barriers
Here is a video on the concept of speciation
There are different types of speciation – based on tempo and based on barriers. Watch the video and learn about the different types
Then watch this video that details the pre and post zygotic barriers
Watch this video for the rate/tempo of speciation
Work through the following topics/questions
1.What is the definition of species and population?
2.Describe the mechanisms by which speciation can occur
3.Explain why there is no gene flow in reproductive isolation. Determine why reproductive isolation is a prerequisite for speciation to occur.
4.When there is a physical barrier created by natural processes such as earthquake, what type of reproductive isolation will it lead to?
5.What are the different types of prezygotic and postzygotic reproductive isolations? Make sure you know them all. In the tests/exams there will be examples given and you will have to identify the type of reproductive isolation. List one of each here with an example.
6.Differentiate between allopatric and sympatric speciation.
7.What is the pace of evolution – fast or slow?
8.Explain the extrinsic and intrinsic reproductive isolation mechanisms.
9.Explain the term divergence. Does accumulation of genetic mutations lead to divergence?
10.Explain adaptive radiation. Determine if Darwin’s finches of Galapagos Island is an example of adaptive radiation?
Population Genetics
This video explains microevolution, macroevolution. Remember, populations evolve not species, gene pool,
You will also be practicing the Hardy Weinberg equation and problems based on it. So if you are interested, then you can watch the part 2 of population genetics described at the end of the 1st video.
1.What is a gene pool?
2.What are the sources of genetic variation in a population?
3.What is an allele frequency and a genetic frequency?